Particle separators are used to remove sand and dust from the air intake of gas turbine engines. A small fraction of the incoming air is often diverted to accomplish scavenging of the sand and dust from the separator. The pump that aids in the scavenging operation has to function in a very contaminated environment since there is a very high concentration of sand and dust in the separator exhaust. Sand particles seriously pit and degrade the performance and life expectancy of a conventional bladed-fan type air pump.
In an earlier invention which issued as U.S. Pat. No. 3,977,811 a pump was disclosed which has a self-bypassing feature. The self-bypassing feature greatly improves rotor durability for air pumps delivering large volumes of sand and dust laden air on a continuing basis. In the method of U.S. Pat. No. 3,977,811 there is still some abrasion of the pump rotor blades. This happens because the inertial dirt deflector system cannot separate out all of the sand and dust particles.
This invention solves the blade erosion problem further by essentially excluding all dust and sand particles from the airstream passing through the rotor blades of the pump. To achieve this separation, advantage is taken of two tasks which must be accomplished in an operating gas turbine engine. One task has to do with scavenging the sand and dust from the separator attached to the air intake of the engine. The other task has to do with cooling the oil passing through the heat exchanger attached to the engine gear case. The air passing through the heat exchanger used for cooling the engine oil is reasonably free from dust and sand. As such it makes a good source of air to draw through a primary flow channel and into the bladed fan portion of a pump. It is therefore the object of this invention to utilize the air drawn through the heat exchanger by accelerating it through an annular shaped ejector nozzle of an air jet pump. The high speed jet of air passing through the ejector nozzle enters a suction chamber which is connected by a secondary flow channel to the scavenge manifold of the sand and dust separator. Presence of the high velocity airstream in the suction chamber draws the sand and dust laden contents of the secondary flow channel into the suction chamber. The entrained contents of the two air sources are then exhausted overboard after passing through an annular diffuser stage.